If you're looking for a Thanksgiving dinner..
To be honest, there aren't that many Montreal restaurants serving Thanksgiving dinner ... I found 3 serving a table d'hôte with turkey:
-B&M: 16$ (from Friday to Monday)
-Le Montrealais (Queen Elisabeth Hotel): 35$ http://www.fairmont.com/queenelizabeth/GuestServices/Restaurants/LeMontrealais.htm
-Globe: 48$ (Sunday + Monday